In general, an electrophotography in a PPC (Plain Paper Copy) copier or a printer for transferring a toner image formed on a photo-sensitive material onto a recording sheet is carried out in a method described below. That is, an electrostatic latent image is formed on a photo-sensitive material, the latent image is developed by using a toner, the toner image is transferred onto a sheet to be fixed such as paper or the like, and then the transferred toner image is fixed by heating with a heat roll or a film. Since the fixation is carried out under heat at a state that the heat roll or the film is directly in contact with the toner on the sheet to be fixed, it is performed in a short period of time and with a very high thermal efficiency, thereby achieving a very good fixing efficiency. However, though having a good thermal efficiency, the heat fixing method has a problem of a so-called offset phenomenon. Namely, since a toner is contacted with the surface of the heat roll or the film in the melt state of the toner, the toner is transferred by adhering on the surface of the heat roll, and the transferred toner is transferred again on the next sheet to be fixed to contaminate it.
In order to obtain a resin excellent in fixing properties and offset resistance, there have been disclosed a high molecular weight resin and a low molecular weight resin used in mixture with each other, and a high molecular weight portion-crosslinked resin (for example, refer to Patent Document 1). Furthermore, in order to achieve low-temperature fixing properties and offset resistance, there has been disclosed a resin with viscoelasticity specified at 160 and 190 degrees centigrade (for example, refer to Patent Document 2). However, further improvement of fixing properties and offset resistance has been in demand.
Meanwhile, in late years, reduced environmental burdens have become an important object. As a method for producing a toner in general, there has been adopted a so-called kneading and grinding method in which a resin, a colorant, a charge controlling agent, a wax and the like are kneaded by the use of a kneader, cooled, finely ground by the use of a grinder, and then dispensed to give a toner. However, in the kneading and grinding method, much energy has been required for a grinding process. Accordingly, the improvement in the productivity has been in demand from the viewpoint of energy saving. By reducing cohesive force of a binder resin, it is possible to reduce grinding energy. However, the deterioration of durability was resulted in, and the productivity and durability of the toner could hardly be achieved.    Patent Document 1: Japanese Patent Laid-open No. 1998-87837    Patent Document 2: Japanese Patent Laid-open No. 1999-282198